Molecular Mechanisms Regulating Carbohydrate Metabolism During Lolium perenne Regrowth Vary in Response to Nitrogen and Gibberellin Supply

The promoting effects of both high nitrogen (N) and exogenous gibberellin (GA) supply on regrowth of Lolium perenne have been widely reported. The mobilisation of carbohydrate reserves in response to N is a critical mechanism for promoting plant regrowth. However, our knowledge about GA regulation of carbohydrate metabolism remains limited. Here, we analysed the effects of both N and exogenous GA on the molecular mechanisms controlling perennial ryegrass regrowth and investigated the similarities and differences. Our analyses show that both high N and exogenous GA supply lead to a decline in the accumulation of carbohydrate reserves, but the regulatory mechanisms responsible for this decline varied between N and GA supply. The effects of elevated N were mainly through declining fructan biosynthesis which results in improving photosynthate use efficiency to promote plant regrowth, whereas the application of exogenous GA resulted in an increase in the hydrolytic activities of fructan exohydrolase and invertases capable of cleaving reserved carbohydrates to release energy sources for plant regrowth.